Non-power shift transmissions in agricultural tractors require starting from a rest position in the gear that will be used for the operation. The reason for this is that when performing some operations, such as soil tillage, de-clutching to shift up allows the tractor to stop. Almost all tractors use a plate type clutch, and because of the requirement that the tractor be able to start under full load, the clutch must be capable of absorbing or dissipating full engine power for some time to provide acceptable durability.
Full power shift transmissions such as that described in my copending application Ser. No. 07/444,312 do not have the same requirements. With tractors having transmissions of this type, the operator normally downshifts to start under heavy loads, or under other conditions where he would slip the clutch on a non-power shift transmission. However, most current power shift transmissions allow using the clutch pedal in an inching function just like a regular clutch pedal in a non-power shift transmission, and the clutches are designed to handle the same conditions as described above.
Some power shift transmission clutches are not designed to handle these conditions and a control system is used which automatically shifts the transmission to low gear when the tractor stops. While this effectively protects the clutch from abuse, it is inconvenient for some operations.